Optical disk, optical disk recording method and optical disk apparatus

ABSTRACT

A signal can be detected based on a level slice system and detection delay time can be reduced by setting the recording density of a header field in a linear direction lower (coarse) than that of a user data recording field. Further, a signal can be detected based on the level slice system and detection delay time can be reduced by using a mark position form having a large detection margin as an information recording system of the header field. A readout error of a sector number due to a detection error is compensated for by recording address marks AM for attaining byte synchronization of the header field in both of a head portion and tail portion of information recorded in the header field.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2000-151421, filed May 23,2000, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an optical disk on which data is recorded, arecording method for recording data on the optical disk, and anapparatus for recording and reproducing data on the optical disk.

Recently, DVD systems have been developed to meet the requirements forrecording MPEG2 images on one surface of an optical disk having adiameter of 12 cm for two hours or more. Present DVD standards statethat the memory capacity of the disk is 4.7 GB for one surface, thetrack density is 0.74 μm/track, and the linear density is 0.267 μm/bit.A DVD based on the above standards is referred to as a present DVD inthis specification.

Reproduction of information recorded on an optical disk such as a DVD isperformed by use of an optical head. In the optical head, a light beamemitted from an LD (laser diode) is focused on a pit series formed onthe track of the optical disk via an object lens, a light beam reflectedfrom the optical disk is concentrated on a photo-detector by use of acondensing lens and thus a reproduction signal can be attained. Thereproduction signal from the photo-detector is input to a reproductionsignal processing system and subjected to waveform equalization by anequalizer, and then data is decoded by use of a detector. According toDVD standards, the wavelength of the LD in the optical head is 0.65 μmand the numerical aperture of the object lens is 0.6.

As a higher definition system is required as an image source, it isrequired to further increase the memory capacity of the DVD in order torecord and supply such image data. In order to satisfy the aboverequirement, the wavelength of the LD is reduced to attain a higherrecording density expressed in terms of the wavelength, thus requiringfurther study on increasing the memory capacity using the PRML (PartialResponse Maximum Likelihood) signal process.

In the conventional signal detection method, whether the recordedinformation is “0” or “1” is determined for each bit. Since the intervalbetween pits or marks becomes shorter as the information recordingdensity is increased, the influence of waveform interference by theadjacent information bit on the reproduction signal also increases.

In order to eliminate the influence of waveform interference, it isnecessary to perform a signal process to emphasize the high frequencycomponent of the response characteristic of the recording/reproductionchannel and suppress the skirt portion of the response waveformextending to the adjacent bit to a low level.

However, since the noise component is also emphasized if the highfrequency component of the response characteristic is emphasized, thenumber of errors caused by the emphasizing process consequentiallyincreases. Therefore, it is difficult to significantly improve therecording density using the conventional signal processing system.

On the other hand, in the PRML signal processing system, a waveforminterference amount between adjacent bits of the reproduction signalwaveform is permitted in a range specified by the PR (Partial response)class. Since the reproduced waveform is influenced by the waveforminterference from the adjacent bit and distorted, it becomes impossibleto determine data by use of only one bit as in the conventional system.

However, since the waveform interference amount is limited to aspecified value, signal power dispersed before and after an informationbit can be efficiently utilized if a Maximum Likelihood detector usingan ML (Maximum Likelihood) determination circuit for selecting data ofthe most likelihood among the sequence by taking portions before andafter the waveform into consideration is used, and therefore, data canbe detected at a relatively low error rate. A PR equalizer is used as anequalizing circuit for correcting a deviation of the reproductionwaveform from the PR class.

In conventional level slice equalizers, the reproduced waveform issubjected to a waveform equalization process to set the intersectingpoint between the equalized waveform and a certain threshold level atthe center of the window. More specifically, the high frequencycomponent of the reproduced signal is amplified. In the detector, anintersecting point between the equalized waveform and the certainthreshold level is detected and if the intersecting point is detected inthe window, binary data “1” is output, and if it is not detected, binarydata “0” is output. Then, by subjecting the binary data obtained afterdetection of the intersecting point to an NRZI (Non Return ZeroInverted) conversion process, the decoded data can be attained.

The intersecting point between the equalized waveform and the thresholdlevel does not always exist at the center of the window due to thepresence of noise. The standard deviation of intersecting point datastandardized according to the window width is called “jitter” and isused as an evaluation standard for optical disks and drive units.

Now, a case wherein an optical disk whose recording density is madehigher than present DVDs is reproduced by use of the same optical headas that of the present DVD is considered. If the track density isincreased, a reproduction signal may contain a large amount ofsignal-degrading component called “crosstalk”. On the other hand, if thelinear density is increased, the reproduced waveform becomes dull. Asdescribed before, in the equalizer, since the high frequency componentof the reproducing signal is amplified, it is necessary to more stronglyamplify the high frequency component when an input reproduced waveformbecomes duller. As a result, the equalizer also amplifies thesignal-degrading component. Thus, if the waveform slice system is usedfor the signal detection system, the signal-degrading component isincreased irrespective of the method for increasing recording density,therefore data cannot be correctly decoded.

As the reproduction signal processing system used when the SNR(signal/noise ratio) of the reproduction signal is lowered, utilizationof a PRML (Partial Response and Maximum Likelihood) system instead ofthe waveform slice system is studied. In the PRML system, the reproducedwaveform is equalized into a waveform having a known correlation betweenidentification points called a PR characteristic by use of theequalizer.

Further, the PRML signal processing system can attain a satisfactory(low) error rate in the case of high recording density. This system is asystem for detecting data by use of the correlation between informationbits while permitting waveform interference. Therefore, a delay occursbecause a sample data series is stored into a bus memory as shown inFIG. 9 which will be described later.

In the process for detecting user data, generally, the above delay doesnot cause any problems. However, in the header field, since a readoutsector number is fed back to the later operation, the influence becomeslarger.

That is, in a data writing process, a sector number is read out from theheader field, and if the number is determined as a to-be-accessedsector, the readout operation must be immediately interrupted, whichaffects the write operation. Further, if the number is not the objectsector, the write operation is disabled since data will be destroyed.Therefore, if detection of the number necessary for the abovedetermination is delayed, it becomes necessary to take a large GAP fieldof FIG. 10 which will be described later in order to take a sufficientlylong time corresponding to the delay time and thus the format efficiencyis degraded accordingly.

In the conventional header field, only one address mark AM for attainingbyte synchronization is provided after VFO. The construction issatisfactory when a clock phase pull-in process is completely terminatedin the VFO field, but if the phase pull-in process is not completelyperformed due to a disturbance, for example, data after this cannot becorrectly read out.

Therefore, it is required to provide a device capable of suppressing thetime delay caused when an address of the header field is read out,reducing the interval of a gap field required between the header fieldand the recording field and improving the format efficiency.

Further, it is required to provide a device capable of error-freereadout of an address of the header field.

This invention can solve the above problems, suppress the time delaycaused when an address of the header field is read out, reduce theinterval of a gap field required between the header field and therecording field and improve the format efficiency.

Further, this invention can read out an address of the header fieldwithout error.

BRIEF SUMMARY OF THE INVENTION

An optical disk of this invention comprises header fields which areprovided on tracks of a concentric form or spiral form and in whichaddresses each indicating a position on the track are previouslyrecorded; and recording fields which respectively follow the headerfields and in which preset data is recorded; wherein the recordingdensity of the header field is lower than that of the recording field.

An optical disk recording method of this invention is a method forrecording data on an optical disk having header fields which areprovided on tracks of a concentric form or spiral form and in whichaddresses each indicating a position on the track are previouslyrecorded, and recording fields which respectively follow the headerfields and in which preset data is recorded; wherein data is recorded inthe recording field with a recording density higher than the recordingdensity of the header field.

An optical disk apparatus of this invention for recording data on anoptical disk having header fields which are provided on tracks of aconcentric form or spiral form and in which addresses each indicating aposition on the track are previously recorded, and recording fieldswhich respectively follow the header fields and in which preset data isrecorded and reproducing data recorded on the optical disk, comprisesfirst reproduction means for reproducing data in the header field;second reproduction means for reproducing data in the recording field;determining means for determining whether a signal now reproduced is asignal from the header field or a signal from the recording field; andprocessing means for reproducing data by use of the first reproductionmeans when the determining means determines that the signal nowreproduced is a signal from the header field and reproducing data by useof the second reproduction means when the determining means determinesthat the signal now reproduced is a signal from the recording field.

An optical disk apparatus of this invention for recording data on anoptical disk having header fields which are provided on tracks of aconcentric form or spiral form and in which addresses each indicating aposition on the track and at least one pattern for detecting the addressare previously recorded, and recording fields which respectively followthe header fields and in which preset data is recorded and reproducingdata recorded on the optical disk, comprises first reproduction meansfor reproducing data in the header field; second reproduction means forreproducing data in the recording field; recording means for recordingdata in the recording field; first detecting means for detecting thepattern used for detecting the address recorded in the header fieldbased on a reproduction signal from the first reproduction means; seconddetecting means for detecting the address recorded in the header fieldbased on a detection process of the first detecting means; andprocessing means for reproducing data in a corresponding portion of therecording field by use of the second reproduction means or recordingdata in a corresponding portion of the recording field by use of therecording means when the address detected by the second detecting meanscomes to an access position.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a view showing the schematic construction of an optical disk;

FIG. 2 is a view for illustrating the state of pre-format data of aheader field of the optical disk and grooves and lands of thesurrounding portion;

FIG. 3 is a diagram for explaining the state of pre-format data of aheader field of the optical disk and grooves and lands of thesurrounding portion;

FIG. 4 is a view for illustrating the state of pre-format data of aheader field of the optical disk and grooves and lands of thesurrounding portion;

FIG. 5 is a diagram for explaining the state of pre-format data of aheader field of the optical disk and grooves and lands of thesurrounding portion;

FIG. 6 is a diagram for explaining the state of pre-format data of aheader field of the optical disk and grooves and lands of thesurrounding portion;

FIG. 7 is a view for illustrating zones of the optical disk;

FIG. 8 is a diagram for explaining ECC block data;

FIG. 9 is a diagram for explaining the frame construction of eachsector;

FIG. 10 is a diagram showing a sector format of each sector;

FIG. 11 is a diagram showing a format of another embodiment of theheader field;

FIG. 12 is a diagram showing the schematic construction of an opticaldisk apparatus;

FIG. 13 is a circuit diagram showing the schematic construction of asignal detecting section and signal determining circuit;

FIG. 14 is a block diagram showing a schematic construction of a levelslice signal processing circuit and PRML signal processing circuit;

FIGS. 15A to 15F are diagrams showing signal waveforms and data valuesat main portions of the level slice signal processing circuit;

FIGS. 16A to 16G are diagrams showing signal waveforms and data valuesat main portions of the PRML signal processing circuit;

FIGS. 17A to 17C are diagrams for illustrating the decoding processusing an ML decoder;

FIGS. 18A to 18D are diagrams showing signal waveforms in the signaldetermining circuit;

FIG. 19 is a diagram showing the schematic construction of an equalizerand ML decoder;

FIG. 20 is a diagram for illustrating a change in the state of ACS;

FIGS. 21A, 21B are diagrams for illustrating a 1,7 modulation process;

FIGS. 22A to 22F are diagrams showing a difference in the data detectionwindow width according to modulation codes;

FIG. 23 is a flowchart for illustrating the data recording process anddata reproducing process;

FIG. 24 is a diagram showing the schematic construction of an opticaldisk apparatus according to another embodiment;

FIG. 25 is a flowchart for illustrating the data recording process anddata reproduction process;

FIG. 26 is a diagram showing the schematic construction of an opticaldisk apparatus according to another embodiment;

FIG. 27 is a block diagram showing the schematic construction of a levelslice signal processing circuit and PRML signal processing circuit;

FIG. 28 is a flowchart for illustrating the data recording process anddata reproducing process;

FIG. 29 is a diagram showing the layout of a header field in anotherembodiment;

FIG. 30 is a diagram showing the circuit construction of an ID detectingsection;

FIG. 31 is a diagram showing the schematic construction of an opticaldisk apparatus according to another embodiment;

FIG. 32 is a flowchart for illustrating the ID detecting process in theID detecting section;

FIG. 33 is a flowchart for illustrating the ID detecting process in theID detecting section;

FIG. 34 is a diagram for illustrating an example of a process fordistributing and recording ID information into a plurality of sectors;and

FIG. 35 is a diagram for illustrating an example of a process fordistributing and recording ID information into a plurality of sectors.

DETAILED DESCRIPTION OF THE INVENTION

There will now be described embodiments of this invention with referenceto the accompanying drawings.

FIGS. 1, 2, 3 show the schematic constructions (one example of the formof a track) of an optical disk 1 of this invention.

The optical disk 1 has grooves 2 which are previously wobbled fortracking and in which data is recorded and header portions (headerfields) 3 having pre-pit (emboss pit) strings each indicating a trackaddress or the like. Lands 4 are provided in positions adjacent to thegrooves 2.

Data is recorded in the groove 2 by use of recording marks 5 based on aphase change. For example, data is recorded by use of the recordingmarks 5 based on the 1,7 RLL (Run Length Limited) modulation process.For example, user data is recorded in the groove 2 based on a mark edgeform.

Data is recorded in the header field 3 by use of pre-pits 6 previouslyformed, for example, formed at the time of formation of the grooves. Forexample, data is recorded by use of the pre-pits 6 based on the 8-16 RLLmodulation process. Further, for example, address data is recorded inthe header field 3 based on a mark position form.

As shown in FIG. 1, the grooves 2 of the optical disk 1 are previouslywobbled in a preset cycle for tracking. For example, grooves for tackingare wobbled in a preset cycle in order to obtain a signal used as areference at the data recording time.

The header field 3 is formed at the time of formation of the grooves. Asshown in FIGS. 2, 3, the header field 3 includes a plurality of headerfields 3 a, 3 b, 3 c, 3 d each formed of a plurality of pits and ispre-formatted with respect to the grooves 2 as shown in FIGS. 2, 3 andthe center of each pit lies on the same line which passes through thecenter of the amplitude of corresponding grooves 2.

The optical disk 1 is explained by taking a case wherein data isrecorded in the grooves as an example, but the optical disk is notlimited to this case and the optical disk in which data can be recordedin both of the lands and grooves may be used (DVD-RAM).

In this case, as shown in FIGS. 4, 5, 6, the optical disk has grooves 7previously wobbled for tracking and header fields 8 having pre-pit(emboss pit) strings each indicating a track address or the like.

That is, the grooves 7 for tacking are wobbled in a preset cycle inorder to obtain a signal used as a reference at the data recording time.

The header field 8 is formed at the time of formation of the grooves. Asshown in FIGS. 5, 6, the header field 8 includes a plurality of headerfields 8 a, 8 b, 8 c, 8 d each formed of a plurality of pits and ispre-formatted with respect to the grooves 7 as shown in FIGS. 5, 6 andthe center of each pit lies on the boundary line between the groove 7and the land 9. FIG. 5 shows the header field 8 attached to the headsector of each track and FIG. 6 shows the header field 8 attached to oneof sectors other than the head sector provided in each track.

In this case, the header fields 8 for the grooves and the header fields8 for the lands are arranged alternately (in a staggered form).

The grooves and lands can be formed in a concentric form instead of thespiral form.

In this embodiment, it is assumed that data is recorded based on a zoneCLV (ZCLV) system. The ZCLV system is a system for dividing theplurality of tracks into several zones and keeping constant the rotatingspeed of the disk in the same zone. The recording frequency is keptconstant for the entire circumference. Therefore, the recording capacityof each track in the same zone is the same. In FIG. 7, the clock signalsfor the respective zones are the same and the rotating speeds of theoptical disk 1 for the respective zones and the numbers of sectors foreach track are different.

In this embodiment, the term “sector” is used to indicate a minimum unitwhich can be used for recording, reproducing and rewriting. In the DVDformat, 16 sectors constitute one ECC block. In the construction of theECC block of the DVD, parity is distributed and recorded in the sectors.

Therefore, data can be rewritten in the sector unit as a binary datastring. However, since a defect occurs in the parity if data of only onesector is rewritten, data can be rewritten only in the ECC block unit assignificant data. In this respect, it can be said that the rewritableunit is an ECC block, but in this embodiment, the “sector” used as aunit to which access of binary data string can be made is called a“minimum recordable unit”.

That is, as shown in FIG. 7, the optical disk 1 is constructed of 35zones, for example, and the rotating speeds (the reference speed foreach zone) of the optical disk 1 for the respective zones and thenumbers of sectors for each track are different.

Each zone includes a plurality of (1568) tracks in the radial direction.

In each zone, the rotation speed of the optical disk 1 becomes lower andthe number of sectors for each track becomes larger in a portion on theinner side of the optical disk than in a portion on the outer side.

As shown in FIG. 8, data is recorded in the tracks of each zone for eachECC (error correction code) block data unit (for example, 38688 bytes)used as a data recording unit.

The ECC block includes 16 sectors in which 2-kilobyte data is recorded,each of sector ID (identification data) items 1 to 16 of 4-byte (32-bit)configuration used as address data is attached to the main data (sectordata) together with an error detection code (IED: ID Error DetectionCode) of 2-byte configuration for each sector, and lateral ECCs (ErrorCorrection Codes) 1 and longitudinal ECCs 2 used as error correctioncodes for reproduction data recorded in the ECC block. The ECCs 1, 2 areerror correction codes attached to data as redundancy words for ensuringreproduction of data in the case that defects exist in the optical disk1.

Each sector is constructed by data of 172 bytes×12 rows, and the lateralECC 1 of 10-byte configuration is attached for each row (line) and thelongitudinal ECC 2 of one row with 182-byte configuration is attached.Thus, an error correcting section 27 which will be described laterperforms an error correction process for each line by use of the lateralECC 1 and performs an error correction process for each column by use ofthe longitudinal ECC 2.

When the ECC block is recorded on the optical disk 1, a sync code (2bytes: 32 channel bits) for taking byte synchronization at the datareproducing time is attached for every preset data amount (for everypreset data length interval, for example, 91 bytes: 1456 channel bits)of each sector.

As shown in FIG. 9, each sector is constructed by 26 frames (frame=91bytes: 1456 channel bits) from frame zero to a 25th frame. The sync code(frame sync signal) attached to each frame is constructed by aspecification code (one byte: 16 channel bits) for specifying a framenumber and a common code (one byte: 16 channel bits) commonly used foreach frame.

FIG. 9 shows the construction of a physical sector in the DVD. It isconstructed by 26 SYNC frames starting from a 32-channel bit SYNC code(sync code) and the channel bits are set to 38688 channel bits in total.

The format of each sector is shown in FIG. 10.

In FIG. 10, one sector is constructed by 2697 bytes and includes a128-byte header field (corresponding to the header section) 3, 8, 2-bytemirror field 10 and 2567-byte recording field 11.

The channel bit recorded in the header field 3, 8 of the sector takes aform subjected to 8-16 RLL modulation. The channel bit recorded in therecording field 11 of the sector takes a form subjected to 1,7 RLLmodulation. In the header field 3, 8, address data is recorded accordingto the mark position form. In the recording field 11, user data isrecorded according to the mark edge form.

The header field 3, 8 is an area in which preset data is recorded whenthe optical disk 1 is formed. The header field 3, 8 is constructed byfour header fields of header 1 field 3 a, 8 a, header 2 field 3 b, 8 b,header 3 field 3 c, 8 c and header 4 field 3 d, 8 d.

Each of the header 1 field 3 a, 8 a to header 4 field 3 d, 8 d isconstructed by 46 bytes or 18 bytes and includes a 36-byte or 8-bytesync code portion VFO (Variable Frequency Oscillator), 3-byte addressmark AM (Address Mark), 4-byte address portion PID (PositionIdentifier), 2-byte error detection code IED (ID Error Detection Code)and one-byte post amble PA (Post Ambles).

The header 1 field 3 a, 8 a and header 3 field 3 c, 8 c include a36-byte sync code portion VFO 1 and the header 2 field 3 b, 8 b andheader 4 field 3 d, 8 d include an 8-byte sync code portion VFO 2.

The sync code portion VFOs 1, 2 are fields for performing the pull-inprocess of the PLL, and the sync code portion VFO 1 is obtained byrepeatedly recording “00010001” in channel bits by 36 bytes (576 bits inchannel bits) (repeatedly recording a pattern with a preset interval)and the sync code portion VFO 2 is obtained by repeatedly recording“00010001” in channel bits by 8 bytes (128 bits in channel bits). Thesync code portion VFO 1 is a successive pattern of so-called 4T.

The address mark AM is a 3-byte sync code indicating a position in whicha sector address starts and is constructed by a 48-bit channel code. Asthe pattern of the respective bytes of the address mark AM, a specialpattern of “000100010000000000000100010001000000000000010001” which doesnot appear in the data portion is used.

The address portion PIDs 1 to 4 are fields in which sector numbers arerecorded as 4-byte addresses. The sector number is a physical sectornumber indicating a physical position on the track of the optical disk1, and since the physical sector number is recorded in the masteringprocess, it cannot be rewritten.

The address portion PID (1 to 4) includes one-byte (8-bit) sectorinformation and 3-byte sector number (physical sector number as aphysical address indicating a physical position on the track). Thesector information includes a 2-bit reserve field, 2-bit physical IDnumber field, 3-bit sector type field and one-bit layer number field.

The physical ID number is “1” in the case of PID 1, for example, and isa number indicating the order in which data is overwritten by four timesin the header field 3, 8.

In the sector type field, codes indicating the first sector and lastsector of the track are recorded.

The error detection code IED is used for the sector address (containingthe ID number) and for detecting whether or not an error is present inthe readout PID.

The post amble PA contains state information necessary for demodulationand also has a function of polarity adjustment for terminating theheader field 51 in space.

The mirror field 10 is used for offset correction of a tracking errorsignal and timing generation of a land/groove changeover signal, forexample.

The recording field 11 includes a 10-byte or 11-byte gap field, 20-byteto 27-byte guard 1 field, 35-byte VFO 3 field, 3-byte pre-synchronouscode (PS) field, 2418-byte data field, one-byte post amble 3 (PA3)field, 48-byte to 55-byte guard 2 field and 24-byte or 25-byte bufferfield.

The gap field is a field in which nothing is written.

The guard 1 field is a field for preventing terminal deteriorationcaused at the repetitive recording time inherent in a phase changerecording medium from giving an influence on the VFO 3 field.

The VFO 3 field is used for repeatedly recording “00010001” in channelbits by 35 bytes (560 bits in channel bits) in the PLL lock field.

The PS (pre-synchronous code) field is a synchronization field forconnection to the data field.

The data field is a field including data ID, data ID error detectioncode IED, sync code, ECC (Error Correction Code), EDC (Error DetectionCode) and user data. The data ID is sector data of 4-byte (32-channelbit) configuration of each sector. The data ID error detection code IEDis an error detection code of 2-byte (16-bit) configuration for data ID.

The PA (post amble) 3 field is a field containing state informationnecessary for demodulation and indicating the end of the last byte ofthe preceding data field.

The guard 2 field is a field which prevents terminal deterioration frominfluencing the data field. Terminal deterioration, inherent in phasechange recording media, is caused by repetitive recording.

The buffer field is a field provided for absorbing variations inrotation of the optical disk 1 so as to prevent the recording field fromextending into the next header field 3, 8.

The reason why the gap field is expressed to be constructed by 10 or 11bytes is that random shifting is performed. Random shifting shifts thedata write starting position to reduce repetitive recording degradationof the phase change recording medium. The length of random shifting isadjusted by use of the buffer field lying in the last portion of therecording field and the total length thereof in one sector is a constant2697 bytes.

Next, anther embodiment of the header field 3, 8 is explained withreference to FIG. 11. Portions which are the same as those of FIG. 10are denoted by the same reference numerals and the explanation thereofis omitted.

The header field 3, 8 includes four header fields of header 1 field 3a′, 8 a′, header 2 field 3 b, 8 b, header 3 field 3 c′, 8 c′ and header4 field 3 d, 8 d.

The header 1 field 3 a′, 8 a′ is constructed by 46 bytes and includes a6-byte sync code portion VFO arranged in the top portion and a 3-byteaddress mark AM, 4-byte address portion PID 1, 2-byte error detectioncode IED 1 and one-byte post amble PA 1 which are repeatedly recorded byfour times after the VFO.

The header 3 field 3 c′, 8 c′ is constructed by 46 bytes and includes a6-byte sync code portion VFO arranged in the top portion and a 3-byteaddress mark AM, 4-byte address portion PID 3, 2-byte error detectioncode IED 3 and one-byte post amble PA 1 which are repeatedly recorded byfour times after the VFO.

Therefore, a total of 10 bytes of AM, PID, IED, PA is repeatedlyrecorded by four times after the 6-byte sync code portion VFO. As aresult, the pull-in time of the PLL becomes longer than in a casewherein only the exclusive VFO pattern (36 bytes) is used, but since thepossibility of reading ID information repeatedly recorded can beenhanced if the margin of the header field is large, it becomes moreadvantageous than the construction of FIG. 10.

Next, an optical disk apparatus 21 for dealing with the optical disk 1is explained with reference to FIG. 12.

The optical disk apparatus 21 records data on the optical disk 1 andreproduces data recorded on the optical disk 1 while it rotates theoptical disk 1 at different speeds for respective zones.

As shown in FIG. 12, the main portion of the optical disk apparatus 21includes an optical pickup section (optical head) 22, level slice signalprocessing circuit 23, PRML signal processing circuit 24, signaldetermining circuit 25, drive control circuit 26, error correctingsection 27, host device interface 28, modulator 29, write compensationcircuit 30, write driver 31, servo controller 32 and spindle motor 33.

The optical pickup section 22 has an object lens 34. In the optical headsection 22, a semiconductor laser unit (not shown) is provided to facethe object lens 34 and energized by the write driver 31 used as a lasercontrol unit to generate laser rays of an appropriate wavelength. Whenthe semiconductor laser unit is energized, laser light properly appliedto the optical head 1 is directed to the object lens 34 and converged onthe optical disk 1 by the object lens 34. Data is written on (creationof a mark string: data is written on the optical disk 1 according to theinterval between variable length marks and the length of each variablelength mark) or reproduced from the optical disk 1 by use of theconverged laser light.

Setting contents of the write driver 31 are set by the writecompensation circuit 30 and are different depending on the reproductionpower for obtaining a reproducing signal, recording power for recordingdata and erasing power for erasing data. The laser light has three powerlevels: the reproduction power, recording power and erasing power, andthe semiconductor laser unit is energized by the write driver 31 so asto emit laser light of appropriate power.

The optical disk 1 is directly carried into the apparatus by use of atray (not shown) or carried into the apparatus after being received intoa disk cartridge (not shown) so that the optical disk 1 will be arrangedto face the object lens 34. A tray motor (not shown) for driving theabove tray is provided in the apparatus. Further, the loaded opticaldisk 1 is rotatably held on the spindle motor 33 by a clamper (notshown) and rotated by the spindle motor 33.

The optical pickup section 22 has a signal detecting section 35. Asshown in FIG. 13, the signal detecting section 35 includes amplifiers 41a, 41 b, 41 c, 41 d for converting current signals of detection signals(Ia, Ib, Ic, Id) from a photo-detector 40 used as a photo-detector fordetecting laser light into voltage signals, an adder 42 a for addingtogether the signals from the amplifiers 41 a, 41 b, an adder 42 b foradding together the signals from the amplifiers 41 c, 41 d, and asubtracter 43 for subtracting the signal output from the adder 42 b fromthe signal output of the adder 42 a.

A signal from the subtracter 43 or an output signal of the signaldetecting section 35 is output to the level slice signal processingcircuit 23 for reproducing data of the header field 3, 8, and to thePRML signal processing circuit 24 for reproducing data of the recordingfield 11 and the signal determining circuit 25.

Further, a servo signal (track error signal, focus error signal) isgenerated by a signal processing circuit (not shown) based on thesignals from amplifiers 81 a, 81 b, 81 c, 81 d and output to the servocontroller 32.

As a method for optically detecting a focus deviation amount, thefollowing methods are given, for example.

[Astigmatism Method]

This is a method for detecting variations in laser light irradiated onto the photo-detector 40 by use of an optical element (not shown) forcausing astigmatism to occur which is disposed on an optical detectionpath of laser light reflected from a light reflecting film or lightreflective recording film of the optical disk 1. The photo-detectingarea is divided into four areas along diagonal lines. A differencebetween the sums of the detection signals obtained from the respectivediagonal detection areas is derived by a signal processing circuit (notshown) and used as a focus error detection signal (focus signal).

[Knife-Edge Method]

This is a method using a knife edge disposed for non-symmetricallyshielding part of the laser light reflected from the optical disk 1. Thephoto-detecting area is divided into to two areas and the differencebetween the detection signals obtained from the respective detectionareas is derived as a focus error detection signal.

Generally, either the astigmatism method or the knife-edge method isused.

The optical disk 1 has tracks in a spiral form or concentric form andinformation is recorded on the track. Information is reproduced orrecorded/erased by tracing a focused light spot along the track. Inorder to stably trace the focused light spot along the track, it isnecessary to optically detect a relative positional deviation betweenthe track and the focused light spot.

As the track deviation detecting method, the following methods aregenerally used.

[Differential Phase Detection Method]

A variation in the intensity distribution of laser light reflected froma light reflecting film or light reflective recording film of theoptical disk 1 on the photo-detector 40 is detected. The photo-detectingarea is divided into four areas along diagonal lines. A phase differencebetween the sums of the detection signals obtained from the respectivediagonal detection areas is derived by a signal processing circuit (notshown) and used as a track error detection signal (tracking signal).

[Push-Pull Method]

A variation in the intensity distribution of laser light reflected fromthe optical disk 1 on the photo-detector is detected. Thephoto-detecting area is divided into two areas and a difference betweenthe detection signals obtained from the respective detection areas isderived and used as a track error detection signal.

[Twin-Spot Method]

For example, a diffraction element is disposed in a light transmissionsystem between the semiconductor laser element and the optical disk 1 todivide light into a plurality of wave surfaces and detect a variation inthe reflected light amount of ±primary diffracted light applied to theoptical disk 1. A photo-detecting area for individually detecting thereflected light amount of +primary diffracted light and the reflectedlight amount of −primary diffracted light is disposed in addition to thephoto-detecting area for detecting the reproducing signal and a trackerror detection signal is obtained by deriving a difference between thedetection signals.

The signal processing system on the reproducing side has two systemsincluding a system (level slice signal processing circuit 23) forprocessing a signal from the header field 3, 8 by use of the level slicesystem having less detection delay and a system (PRML signal processingcircuit 24) for processing a signal from the recording field 11 forrecording user data by use of the PRML signal processing system whichcan attain high-density recording.

As shown in FIG. 14, the level slice signal processing circuit 23includes an AGC (Automatic Gain Control) amplifier 51, adder 52,equalizer 53, level slice detector 54, PLL circuit 55, 8-16 RLLdemodulator 56, AGC controller 57 and offset controller 58.

The AGC amplifier 51 corrects the level of a signal from the signaldetector 35 according to a control signal from the AGC controller 57 andoutputs the corrected signal to the adder 52. The adder 52 adds thesignal from the AGC amplifier 51 with an offset signal from the offsetcontroller 58 and outputs the result of addition to the equalizer 53.

The equalizer 53 subjects the waveform (reproduced waveform) of thereproduction signal from the adder 52 to waveform equalization so thatan intersecting point between the equalized waveform and a certainthreshold level will be set at the center of the window and then outputsthe result of equalization to the level slice detector 54, AGCcontroller 57 and offset controller 58.

The level slice detector 54 detects an intersecting point between theequalized waveform from the equalizer 53 and the threshold levelaccording to a channel clock from the PLL circuit 55, and if theintersecting point is detected in the window, binary data “1” is outputto the 8-16 RLL demodulator 56, and if the intersecting point is notdetected in the window, binary data “0” is output to the 8-16 RLLdemodulator 56.

The PLL circuit 55 generates a channel clock based on a signal from thelevel slice detector 54 and outputs the channel clock to the 8-16 RLLdemodulator 56.

The 8-16 RLL demodulator 56 demodulates binary data from the level slicedetector 54 based on the 8-16 RLL code.

The AGC controller 57 corrects the signal of the AGC amplifier 51 basedon the equalized waveform from the equalizer 53.

The offset controller 58 outputs an offset value to the adder 52 basedon the equalized waveform from the equalizer 53.

The waveform slice system used as the signal processing system by thelevel slice signal processing circuit 23 is explained with reference tothe operation waveform diagrams of FIGS. 15A to 15G.

As shown in FIG. 15C, a pit series is previously recorded on the opticaldisk 1 according to the recording waveform of NRZI form shown in FIG.15B and corresponding to recording data which is information to berecorded as shown in FIG. 15A.

When information thus recorded on the optical disk 1 is reproduced, alight beam for reproduction from a photo-diode in the optical pickupsection 22 is applied to the optical disk 1 as a fine beam spot asindicated by a hatched portion in FIG. 15C to read out the pit seriesand derive a reproducing signal.

The waveform (reproduced waveform) of the reproduction signal is notobtained as a rectangular wave such as a recording waveform as shown inFIG. 15B because of the characteristic of the recording/reproducingsystem and is obtained as a dull waveform as shown in FIG. 15D.

Therefore, the reproduced waveform is subjected to waveform equalizationin the equalizer 53 so that an intersection point between the equalizedwaveform and a preset threshold level (indicated by a dashed line) willbe set at the center of the window. More specifically, the highfrequency component of the reproduction signal is amplified.

As shown in FIG. 15F, the level slice detector 54 detects anintersection point between the equalized waveform and the thresholdlevel, and if the intersection point is detected in the window, itoutputs binary data “1”, and if the intersection point is not detectedin the window, it outputs binary data “0”.

Thus, the 8-16 RLL demodulator 56 demodulates the binary data from thelevel slice detector 54.

As shown in FIG. 14, the PRML signal processing circuit 24 includes anAGC amplifier 61, adder 62, A/D converter 63, equalizer (linearequalizer) 64, ML decoder (Viterbi decoder) 65, 1,7 RLL demodulator 66,PLL circuit 67, AGC controller 68 and offset controller 69.

The AGC amplifier 61 corrects the level of a signal from the signaldetector 35 according to a control signal from the AGC controller 68 andoutputs the corrected signal to the adder 62. The adder 62 adds thesignal from the AGC amplifier 61 with an offset signal from the offsetcontroller 69 and outputs the result of addition to the A/D converter63. The A/D converter 63 converts the signal from the adder 62 into adigital signal of a discrete time and discrete amplitude seriesaccording to a channel clock from the PLL circuit 67 and outputs thedigital signal to the equalizer 64.

The equalizer 64 is constructed of a linear equalizer which is formed ofan FIR filter (transversal filter), performs an equalizing process forthe waveform (reproduced waveform) of the reproduction signal from theA/D converter 63 into a waveform of PR(1,1) characteristic and outputsthe equalized waveform to the ML decoder 65, PLL circuit 67, AGCcontroller 68 and offset controller 69.

The ML decoder 65 is constructed by a Viterbi decoder, decodes theequalized waveform from the equalizer 64, detects the same as binarydata and outputs the binary data to the 1,7 RLL demodulator 66.

The 1,7 RLL demodulator 66 demodulates the decoded binary data from theML decoder 65 based on the 1,7 RLL code.

The PLL circuit 67 generates a channel clock based on the signal fromthe equalizer 64 and outputs the channel clock to the A/D converter 63.That is, it recovers the channel clock by converting a differencebetween the amplitude of the PR equalized waveform and an idealamplitude value into a phase difference.

The AGC controller 68 corrects the signal in the AGC amplifier 61 basedon the equalized waveform from the equalizer 64.

The offset controller 69 outputs an offset value to the adder 62 basedon the equalized waveform from the equalizer 64.

Next, the signal processing system by the PRML signal processing circuit24 is explained with reference to the waveform diagrams shown in FIGS.16A to 16G.

A pit series is previously recorded on the optical disk 1 as shown inFIG. 16C according to the recording waveform of NRZI form shown in FIG.16B and corresponding to recording data which is information to berecorded as shown in FIG. 16A.

When information thus recorded on the optical disk 1 is reproduced, alight beam for reproduction from the photo-diode in the optical pickupsection 22 is applied to the optical disk 1 as a fine beam spot asindicated by a hatched portion in FIG. 16C to read out the pit seriesand derive a reproducing signal.

The waveform (reproduced waveform) of the reproducing signal is notobtained as a rectangular wave such as a recording waveform as shown inFIG. 16B because of the characteristic of the recording/reproducingsystem and is obtained as a dull waveform as shown in FIG. 16D.

Waveforms obtained after subjecting the reproduced waveform of FIG. 16Dto waveform equalization based on the PR(1,1) characteristic, PR(1,2,1)characteristic and PR(1,2,2,1) characteristic in the equalizer 64 arerespectively shown in FIGS. 16E, 16F, 16G. The PR(1,1) characteristic isa characteristic in which an impulse response appears at the rate of 1:1at two successive identification points (=amplitude values of thereproduced waveform at two channel clock timings).

The recording waveform of NRZI form of FIG. 16B corresponding to thefirst part “010010” of recording data of FIG. 16A is expressed asfollows.

011100

Since the reproduced waveform is regarded as being an impulse responseto “1” of the recording waveform, the waveform of FIG. 16E expressed aslinear superposition of the following responses and obtained as “012210”becomes a target waveform to be equalized as the PR(1,1) characteristic(class).

0110

00110

000110

The PR(1,2,1) characteristic is a characteristic in which an impulseresponse appears at the rate of 1:2:1 at three successive identificationpoints. The PR(1,2,2,1) characteristic is a characteristic in which animpulse response appears at the rate of 1:2:2:1 at four successiveidentification points. As in the case of the PR(1,1) characteristic,to-be-equalized target waveforms derived by linear superposition ofimpulse responses corresponding to the recording waveform become thewaveforms as shown in FIGS. 16F, 16G (although not shown in the drawing,this is also applied to other PR characteristics).

As shown in FIGS. 16E, 16F, 16G, it is understood that thecharacteristic of the waveform after equalization becomes a dullercharacteristic in the order of PR(1,1) characteristic→PR(1,2,1)characteristic→PR(1,2,2,1) characteristic.

In the PRML system, an increase in the signal degrading component in theequalizer 64 can be suppressed by equalizing the reproduced waveforminto a waveform of a PR characteristic which is closer to thecharacteristic of the reproduced waveform.

In the reproduction signal processing system of PRML system, a Viterbidecoder which is a representative one of maximum likelihood decoders isgenerally used as the ML decoder 65 arranged after the equalizer 64.

If the reproduced waveform is equalized into a waveform of thePR(1,2,2,1) characteristic by the equalizer 64, the ML decoder 65selects a series having the smallest error with respect to the sampleseries of the equalized waveform from all of the reproduced waveformseries which satisfy the PR(1,2,2,1) characteristic and estimates andoutputs recording data (binary data, decoded data) used as a source forgenerating the selected reproduced waveform series while tracing thestate transition.

The state is shown in FIGS. 17A to 17C. In the PRML system, since thedecoding process is not effected based on one sample value but based ona sequence using the correlation (waveform interference) due to the PRcharacteristic of a series of a plurality of sample values as a premise,the PRML system is highly resistant to the signal degrading componenthaving no correlation between sample values.

The signal determining circuit 25 determines whether a signal nowreproduced is a signal from the header field 3, 8 or a signal from therecording field 11 in which user data is recorded.

As shown in FIG. 13, the signal determining circuit 25 includes aband-pass filter (BPF) 71, comparator (Comp) 72 and re-triggerablemultivibrator 73. The re-triggerable multivibrator 73 is supplied with apower supply voltage via a circuit including resistors R1, R2 andcapacitor C.

The signal determining circuit 25 receives a signal from the signaldetector 35 of the optical pickup section 22 and makes the determinationand outputs the result of determination to the drive control circuit 26.

For example, in a case of groove 2 in which data is recorded in theheader field 3, 8 by use of pre-pits and the recording field 11 of userdata is wobbled, if a signal [(Ia+Ib)−(Ic+Id)] of the photo-detector 40as shown in FIG. 13 is input to the signal detector 35 shown in FIG. 13,a determination signal corresponding to the recording field 11 forrecording user data can be obtained as shown by the waveform of FIG.18D, and therefore, the drive control circuit 26 determines whether itis the recording field 11 or not based on the determination signal.

As shown in FIG. 18A, that is, the band-pass filter (BPF) 71 outputs awaveform having an amplitude based on the wobbled groove 2 to thecomparator (Comp) 72. When the comparator (Comp) 72 is supplied with thewaveform of amplitude from the band-pass filter (BPF) 71, it outputs apulse signal as shown in FIG. 18C to the re-triggerable multivibrator 73based on a comparison voltage V1 shown in FIG. 18B. The re-triggerablemultivibrator 73 outputs a determination signal as shown in FIG. 18D tothe drive control circuit 26 based on the pulse signal from thecomparator 72.

Thus, a convex portion of the wobble signal shown in FIG. 18A isdetected by the comparator 72 and a detection signal shown in FIG. 18Cis used as a trigger signal of the re-triggerable multivibrator 73, andan output of the re-triggerable multivibrator 73 is set at “1” as shownin FIG. 18D while the convex portion of the wobble signal is beingdetected.

The error correcting section 27 is constructed by an ECC decoder,corrects errors in the demodulated data from the 8-16 RLL demodulator 56of the level slice signal processing circuit 23 and outputs thecorrected data to the drive control circuit 26 as data of the headerfield 3, 8 or corrects an ECC error of demodulated data from the 1,7 RLLdemodulator 66 of the PRML signal processing circuit 24 and outputs thecorrected data to the host device interface 28 as reproducing data fromthe recoding field 11.

The host device interface 28 outputs reproduction data from the errorcorrecting section 27 to a host device (not shown), outputs aninstruction of recording or reproduction and the access position fromthe host device to the drive control circuit 26, or converts recordingdata from the host device into data of a data form having an errorcorrection code added thereto by an ECC encoder (not shown) and outputsthe converted data to the modulator 29.

The modulator 29 encodes data supplied from the host device interface 28into a 1,7 modulation code or data to be recorded on a channel andoutputs the coded data to the write compensating circuit 30 used as arecording compensator. The write compensating circuit 30 converts anoutput waveform from the modulator 29 into an NRZI form and outputs awrite current waveform in which a deviation between the write waveformand the mark form caused by conduction of heat of the optical disk 1 iscompensated for to the write driver 31.

The drive control circuit 26 controls the whole portion of the opticaldisk apparatus 21.

The drive control circuit 26 supplies a selection signal to the levelslice signal processing circuit 23 or PRML signal processing circuit 24according to the determination signal from the signal determinationcircuit 25 and performs the control operation so that data now producedcan be adequately processed.

For example, the drive control circuit 26 outputs a selection signal toa changeover switch 59 of the level slice signal processing circuit 23to turn ON the changeover switch 59 so that demodulated data from the8-16 RLL demodulator 56 can be output to the error correcting section 27via the changeover switch 59.

Further, the drive control circuit 26 outputs a selection signal to achangeover switch 70 of the PRML signal processing circuit 24 to turn ONthe changeover switch 70 so that demodulated data from the 1,7 RLLdemodulator 66 can be output to the error correcting section 27 via thechangeover switch 70.

In addition, the drive control circuit 26 controls the servo controller32 based on address data including data from the error correctingsection 27 and instruction data from the host device so as to move thelight beam from the optical pickup section 22 to the access position andcontrol the spindle motor 33 to rotate at a rotation speed of a zonecorresponding to the access position.

Further, the drive control circuit 26 controls the write driver 31 so asto control a semiconductor laser oscillator (not shown) based onrecording data from the write compensating circuit 30 to emit a lightbeam.

The drive control circuit 26 includes an AM detector 26 a, SYNC detector26 b and format controller 26 c.

The AM detector 26 a detects an address mark AM of the header field 3, 8according to a demodulation signal from the 8-16 RLL demodulator 56based on the channel clock from the PLL circuit 55 of the level slicesignal processing circuit 23.

For example, the AM detector includes a register in which the pattern ofthe address mark AM is stored, a register for recording a demodulationsignal from the 8-16 RLL demodulator 56 based on the channel clock fromthe PLL circuit 55 and a comparator for comparing register data items inthe two registers and outputs a detection signal of the address mark AMto the format controller 26 c when a coincidence signal is output fromthe comparator.

The SYNC detector 26 b detects a SYNC code of the recording field 11according to a demodulation signal from the 1,7 RLL demodulator 66 basedon the channel clock from the PLL circuit 67 of the PRML signalprocessing circuit 24.

For example, the SYNC detector includes a register in which the patternof the SYNC code is stored, a register for recording a demodulationsignal from the 1,7 RLL demodulator 66 based on the channel clock fromthe PLL circuit 67 and a comparator for comparing register data items inthe two registers and outputs a detection signal of the SYNC code to theformat controller 26 c when a coincidence signal is output from thecomparator.

The format controller 26 c determines a position illuminated on thetrack by the laser light from the optical pickup section 22 and controlstimings of the control signals output to the respective sections byusing the result of determination as a reference by counting a readclock, write clock or wobble clock while attaining synchronization byuse of a detection signal of the address mark AM from the AM detector 26a and a detection signal of the SYNC code from the SYNC detector 26 b.

The read clock is a clock at the data reproducing (readout) time, thechannel clock from the PLL circuit 55 is supplied to the formatcontroller 26 c when data of the header field 3, 8 is reproduced and thechannel clock from the PLL circuit 67 is supplied to the formatcontroller 26 c when data of the recording field 11 is reproduced.

The write clock is a clock generated based on a clock having a presetcycle from a clock generating section (not shown), that is, a referenceclock from an oscillator and supplied to the format controller 26 c.

The wobble clock is a clock generated from a clock generating section(not shown) based on an output signal from the signal detector 35 of theoptical pickup section 22 and supplied to the format controller 26 c.

That is, the format controller 26 c determines a position illuminated onthe track by the laser light from the optical pickup section 22 andcontrols timings of the control signals output to the respectivesections by using the result of determination as a reference by countingthe read clock or wobble clock while attaining synchronization by use ofa detection signal of the address mark AM of the header field 3, 8 and adetection signal of the SYNC code of the recording field 11 when data ofthe recording field 11 is read out.

Further, the format controller 26 c determines a position illuminated onthe track by the laser light from the optical pickup section 22 andcontrols timings of the control signals output to the respectivesections by using the result of determination as a reference by countingthe read clock or wobble clock while attaining synchronization by use ofa detection signal of the address mark AM of the header field 3, 8 whendata of the recording field 11 is written and by counting the writeclock or wobble clock in the recording field 11.

With the construction shown in FIGS. 13, 14, since data of the headerfield 3, 8 is constructed by pre-pits, the write data modulator 29 isonly required to cope with a (1,7) RLL code used in the PRML system ofthe recording field 11.

The signal processing system on the reproducing side is constructed bytwo systems including a system for processing the header field 3, 8according to the level slice system and a system for processing therecording field 11 for recording user data according to the PRML signalprocessing system, but in the above embodiment, since an 8-16 modulationcode in which the minimum run length is 3 is used as the modulation codeof the header field 3, 8, it becomes necessary to provide thedemodulator 56 for the 8-16 RLL modulation code in the succeeding stageof the signal processing system of the level slice system. Further,since a (1,7) modulation code in which the minimum run length is 1 isused as the modulation code of the recording field 11 for recording userdata, it becomes necessary to provide the demodulator 66 for the (1,7)RLL modulation code in the succeeding stage of the signal processingsystem of the PRML system.

FIG. 19 is a diagram showing the construction of the linear equalizer(PR equalizer) 64 and ML decoder (Viterbi decoder, ML detector) 65 whichare the main portions of the PRML signal processing circuit 24.

The ML decoder 65 selects a series having the smallest error withrespect to the sample series of the equalized waveform and outputsbinary data (decoded data) corresponding to the selected series.

That is, as shown in FIGS. 17A to 17C, in a case where the signalwaveform series obtained after PR(1,2,2,1) equalization is given asfollows,

01355311356531 . . .

impulse responses for a candidate of recorded data (01010 . . . ) (therecorded waveform is 01100 . . . ) are given as follows.

012210 . . .

001221 . . .

Then, the reproduced waveform of an ideal PR characteristic obtained bylinear superposition of the above impulse responses is obtained asfollows.

013431 . . .

Further, impulse responses for a candidate of another recorded data(01110 . . . ) (the recorded waveform is 01110 . . . ) are given asfollows.

0122100 . . .

0012210 . . .

0001221 . . .

Then, the reproduced waveform of the ideal PR characteristic obtained bylinear superposition of the above impulse responses is obtained asfollows.

0135531 . . .

After this, the cross-correlations with respect to the waveform seriesof the above reproduced waveforms are calculated and a series having thehighest correlation (=the smallest error between the series) withrespect to the reproduced equalized waveform is selected by aprobabilistic method.

The number of candidates of the waveform can be increased and counted upas in a tree structure but the number of available states is limitedwhen taking the PR characteristic into consideration. In the case of thePR(1,2,2,1) characteristic, the constraint length (the range which thewaveform interference gives an influence) is “4” and variations ofrecording data series caused by the waveform interference occur in 16combinations of four-digit values constructed by two types of datavalues of “0” and “1”, and therefore, the state number having noredundancy is 16 at maximum. There is a possibility that the statenumber will be reduced if the modulation code is limited.

The ML decoder 65 calculates the probability according to an inputsample value when it is assumed that the state is transited from acertain state to a next state. When a plurality of candidates of thewaveform series transited to the same state are provided, a probable oneof the candidates is determined based on the accumulated value of thepast transition probability.

For this purpose, a pass memory 65 d for storing candidates of thewaveform series is provided in the ML decoder 65. Generally, the lengththereof is set to a length of several ten channel bits. A plurality ofcandidates of the waveform series are transited to the same state whilethey pass through the pass memory 65 d, then the candidates arerepeatedly selected and the most probable series is finally selected.

A branch metric calculating section 65 a calculates a logarithm value ofthe probability of transition of the state which is expressed in termsof a difference between actual amplitude and ideal amplitude obtained ifit is assumed that the state is transited from a certain state to a nextcandidate state when a sample value is input. A pass metric memory 65 cis a memory for storing a past branch metric accumulated value obtaineduntil the state transition for each of the states of the state number isrepeatedly effected and the state is attained.

An ACS 65 b is the abbreviated name of a circuit for performing the Add(addition), Compare (comparing) and Selection (selecting) operations. Asshown in FIG. 20, it is assumed that the pass metric values of thestates A and B at time 1 are respectively set at “5” and “8”, the branchmetric caused for transition from the state A (at time 1) to the state Aat time 2 is “4”, the branch metric caused for transition from the stateA (at time 1) to the state B is “5”, the branch metric caused fortransition from the state B (at time 1) to the state A is “2”, and thebranch metric caused for transition from the state B (at time 1) to thestate B is “5”.

In the ACS 65 b, a value “9” obtained by adding the pass metric value“5” of the state A at time 1 with the branch metric “4” caused fortransition from the state A (at time 1) to the state A (at time 2) and avalue “10” obtained by adding the pass metric value “8” of the state Bat time 1 with the branch metric “2” caused for transition from thestate B (at time 1) to the state A (at time 2) are compared with eachother and transition from the state B (at time 1) to the state B (attime 2) corresponding to the larger value is selected (in practice,since the metric value is diverged if a larger value is selected, acircuit for making a calculation in which the metric value correspondingto a higher probability takes a smaller value by properly dealing withthe equations and selecting a smaller metric value is mounted in manycases). Likewise, a value “10” obtained by adding the pass metric value“5” of the state A at time 1 with the branch metric “5” caused fortransition from the state A (at time 1) to the state B (at time 2) and avalue “13” obtained by adding the pass metric value “8” of the state Bat time 1 with the branch metric “5” caused for transition from thestate B (at time 1) to the state B (at time 2) are compared with eachother and transition from the state B (at time 1) to the state B (attime 2) corresponding to the larger value is selected. In this case,since it is only the state B of time 1 that has been transited to eachof the states of time 2, the waveform series which is set to the state Aat time 1 is eliminated from the candidate to be selected. The passmemory 65 d is a memory for recording series (=pass) remaining asselected candidates. Generally, only one candidate of the series is leftbehind by the time the candidate passes through the pass memory 65 d,but a plurality of series may remain as candidates depending on thenoise condition, and in this case, the series which is determined as themost probable candidate is selected by comparing the contents of thepass memory 65 d and the pass metric of the pass metric memory 65 c byuse of the pass selecting section 65 e.

Since the series is selected and detection data is determined after theseries has passed through the pass memory 65 d, an output of the MLdecoder 65 is more delayed than in a case of the conventional datadetector of a waveform slice system.

In the above embodiment, data of the header field 3, 8 is detected bythe level slice system having less detection delay and data of therecording field 11 for recording user data is detected by the PRMLsystem capable of attaining the high recording density. In the case ofthe PRML system, a system such as the 1,7 modulation code in which thecode rate can be made high and the channel band can be suppressed to alow level is used.

The 1,7 modulation code is a conversion system for conversion to a codein which the code rate is 2/3, the minimum run length (=d constraint)indicating the minimum number of “0s” lying between “1” and “1” of thedata series is “1”, and the maximum run length (=k constraint)indicating the maximum number of “0s” lying between “1” and “1” of thedata series is “7”.

As the modulation code adequately applied to the PRML system and havingthe code rate of 2/3 (2 to 3, conversion of 2-bit data to 3 bits), an8-12 modulation code having the d constraint of 1 is provided inaddition to the 1,7 modulation code.

On the other hand, in the case of the level slice system, a system suchas a 2,7 modulation code in which the code rate is low, but the minimumrun length can be set large is preferable. The 2,7 modulation code is aconversion system for conversion to a code in which the code rate is1/2, the minimum run length (=d constraint) indicating the minimumnumber of “0s” lying between “1” and “1” of the data series is “2”, andthe maximum run length (=k constraint) indicating the maximum number of“0s” lying between “1” and “1” of the data series is “7”. As themodulation code adequately applied to the level slice system and havingthe minimum run length (=d constraint) of “2”, an 8-16 modulation codehaving the code rate of 8/16 and an 8-15 modulation code having the coderate of 8/15 are provided in addition to the 2,7 modulation code.

The reason why the system in which the minimum run length can be set toa large value can be adequately used for the level slice system is thatit is important that the linear convolution is established even when theminimum mark/pit amplitude value is small in the case of PRML system,but it is impossible to slice the amplitude if the minimum mark/pitamplitude value is not larger than a certain value in the case of levelslice system.

The 1,7 modulation code is a modulation code in which the code rate is2/3, the d constraint is “1” and the k constraint is “7”. As shown inFIG. 21A, the d constraint of “1” indicates that the constraint is setso as to provide at lest one “1” between “1” and “1” of the code aftermodulation. The k constraint of “7” indicates that the constraint is setso as to provide seven “0s” at most between “1” and “1” of the codeafter modulation. Since the modulated code is recorded in the NRZI form(FIG. 21B) when it is recorded on the optical disk 1, the minimumpit/mark length is set to the length of two channel clocks period andthe maximum pit/mark length is set to the length of eight channel clocksperiod.

The 8-16 modulation code used in the DVD is a modulation code in whichthe code rate is 1/2, the d constraint is “2” and the k constraint is“10”. Therefore, when the code is recorded on the recording medium, theminimum pit/mark length is set to the length of three channel clocksperiod and the maximum pit/mark length is set to the length of elevenchannel clocks period. Like the 8-16 modulation code, in the 8-15modulation code, the d constraint is “2” and the minimum pit/mark lengthis set to the length of three channel clocks period.

If the same user data recording density is set for the 1,7 modulationcode and 8-16 modulation code, 2-bit user data is converted into a 3-bitcode in the 1,7 modulation code and 2-bit user data is converted into a4-bit code in the 8-16 modulation code, and therefore, the length of onechannel clock in the 8-16 modulation code becomes 3/4 times that of the1,7 modulation code. However, since the minimum pit/mark length of the8-16 modulation code is set to the length of three channel clocks periodand the minimum pit/mark length of the 1,7 modulation code is set to thelength of two channel clocks period, the result of (3/4×3/2=9/8) isobtained. Thus, it is understood that the 8-16 modulation code has aslightly larger bit length and is more suitably used for the level slicesystem. Therefore, in order to use the level slice system having lessdetection delay for the header field 3, 8, it is required to make therecording density in the linear direction of information recorded in theheader field 3, 8 lower than the recording density in the lineardirection of information recorded in the user data recording field 11.

In the above example, a case wherein the 8-16 modulation code is usedfor the header field 3, 8 and the 1,7 modulation code is used for theuser data recording field 11 is explained as a code selection examplebased on the reality, but the same modulation code can be used for theheader field 3, 8 and the user data recording field 11 in certain cases.Also, in this case, since it is impossible to operate the level slicesystem at the same amplitude value as the PRML system with the recordingdensity at which the PRML system can be used for the user data recordingfield 11, it becomes necessary to lower the recording density in thelinear direction of the header field 3, 8 and elongate the pit/marklength to attain a large amplitude value.

As an example of a method for using the same modulation code for theheader field 3, 8 and user data recording field 11 and lowering therecording density in the linear direction of the header field 3, 8 toelongate the pit length or mark length and attain a large amplitudevalue, a method for writing data in which a code of the minimum pitlength does not appear into the header field 3, 8 is provided.

The advantage of this method is that the channel clock rate becomes thesame in the header field 3, 8 and user data recording field 11 althoughthe physical pit recording density is lowered. Therefore, it becomesunnecessary to separate the PLL for clock recovery for the header field3, 8 and the PLL for clock recovery for the user data recording field11. Further, since the modulation code is the same, the demodulator canbe commonly used.

In a recording/reproducing optical disk apparatus using a pre-pit headerfor the header field 3, 8, there is a large difference between the levelof a signal from the mark of the user data recording field 11 and thelevel of a signal from the pit of the header field 3, 8. Since the PRMLsignal processing system is a system for detecting an amplitude value atan identification point synchronized with the channel clock, it tends tobe influenced by a level variation. Of course, a correction for leveldifference between the header field 3, 8 and the user data recordingfield 11 is made by use of an AGC, but it is difficult to completelyeliminate the influence by the previously used level at the changeovertime if the detection system utilizes the same PRML signal processingsystem.

Since it is necessary to make the GAP field for changeover large inorder to almost completely eliminate the influence, the formatefficiency is lowered. If the conventional level slice system is appliedto the ID section of the recording/reproduction optical disk apparatususing the pre-pit header, it is expected that the above problem can besolved.

As shown in FIGS. 22A to 22C, data is recorded in the header field 3, 8by use of a modulation code having the minimum pit (mark) length ofthree channel bits and, as shown in FIGS. 22D to 22F, data is recordedin the recording field 11 by use of a modulation code having the minimumpit (mark) length of two channel bits.

That is, FIGS. 22A to 22C show the relation between the channel bitpattern (FIG. 22A), write current waveform (FIG. 22B) and to-be-writtenpit (mark) (FIG. 22C) in the case of the minimum pit in the (1,7)modulation code.

FIGS. 22D to 22F show the relation between the channel bit pattern (FIG.22D), write current waveform (FIG. 22E) and to-be-written pit (mark)(FIG. 22F) in the case of the minimum pit in the 8-16 modulation code.

In a modulation code such as the 8-16 modulation code shown in FIGS. 22Dto 22F in which the code rate is low, the clock frequency becomes highand the width of the data detection window becomes narrow even if theminimum pit/mark length is large.

As for the conversion ratio in the case of 8-16 modulation, one-bit userdata is converted into a 2-bit channel bit pattern from the viewpoint ofratio, and in the case of (1,7) modulation in which the code rate ishigher, 2-bit user data is converted into a 3-bit channel bit pattern.

Therefore, as indicated by the relationship shown in FIGS. 22A to 22Cand FIGS. 22D to 22F, even if the minimum pit (mark) length is larger inthe 8-16 modulation and the amplitude can be made larger than in the(1,7) modulation accordingly, the window width is shorter in the 8-16modulation than in the (1,7) modulation and it becomes more difficult tocontrol the rise and fall positions of the waveform.

If the recording density is enhanced, it is advantageous to use the markedge form in which information can be recorded on both edges in acondition that the recording density is restricted by the minimumpit/mark length, but if an attempt is made to attain a sufficientlylarge margin by lowering the recording density, it is expected that thereliability can be enhanced by using a mark position form in whichinformation is recorded only in the mark position and simplifying theconstruction of the data recording and reproducing means.

That is, pre-pits are formed in the header field 3, 8 by the recordingmethod of the mark position form and recording marks are written intothe user data recording field 11 by the recording method of the markedge form.

As shown in FIG. 2, in the case of the groove recording system, thegroove is interrupted (temporarily terminated) in a portion of thepre-pit header of the header field 3 in some cases.

Further, as shown in FIG. 4, in the case of the groove/land recordingsystem, the groove is interrupted in a portion of the pre-pit header ofthe header field 8 in some cases.

That is, in the case of a wobble groove system for wobbling the groovein the radial direction, timing is generated by use of a clocksynchronized with wobbling. Therefore, if a deviation occurs withrespect to the phase of the clock before the wobble groove isinterrupted and after the wobble groove is re-started, the PLL pull-inprocess becomes necessary and stability cannot be maintained.

Therefore, even when the recording density and minimum pit/mark lengthare changed for the header field 3, 8 and the recording field 11, thelength of the to-be-interrupted groove of the header field 3, 8 is setto the integral multiple of the groove cycle. Alternatively, the phaseof the amplitude at timing when the wobble groove is re-started afterthe header field 3, 8 is set to a value which can be derived based onthe phase at the end time of the wobble groove and the interruption timelength by the header field 3, 8.

That is, an output of a phase difference detection circuit (not shown)of the PLL circuits 55, 67 synchronized with the wobble signal beforeinterruption of the wobble groove is set to have such a phase that alarge phase difference will not be detected when the wobble signal isinput after interruption.

If the recording density is lowered (coarse) to make the pit/mark lengthlarge, a sufficiently large amplitude value can be surely obtained, butin the case of level slice system, the detection window width isimportant as well as the amplitude value.

In a DVD, the pit/mark recording system on the optical disk 1 is a markedge form in which information is recorded in rise and fall positions ofthe waveform. As shown in FIG. 22B, in the modulation code such as the8-16 modulation code in which the code rate is low, the clock frequencybecomes high and the data detecting window width becomes narrow even ifthe minimum pit/mark length is large. That is, it is difficult tocontrol the rise and fall positions of the waveform. If the recordingdensity is enhanced (dense), it is advantageous to use the mark edgeform in which information can be recorded on both ends in a conditionthat the recording density is restricted by the minimum pit/mark length.However, if an attempt is made to attain a sufficiently large margin bylowering the recording density, it is expected that the reliability canbe enhanced by using a mark position form in which information isrecorded only in the mark position and simplifying the construction ofthe data recording and reproducing means.

That is, as shown in FIGS. 2, 4, pre-pits are formed in the header field3, 8 by the recording method of the mark position form and recordingmarks are written into the user data recording field 11 by the recordingmethod of the mark edge form.

Next, with the above construction, the data recording process and datareproduction process in the optical disk apparatus 21 are explained withreference to the flowchart shown in FIG. 23.

Immediately after the seeking operation of the optical pickup section 22is completed or, when the format controller 26 c deviates from thetracing path by a disturbance or the like, that is, when the formatcontroller 26 c cannot grasp the position on the track, the followingcontrol process is effected.

That is, the signal determining circuit 25 checks the signal level of asignal supplied from the optical pickup section 22 (ST1) and determineswhether or not it is the recording field 11 for recording user data(ST2).

As the result of determination, if the signal determining circuit 25determines that it is the user data recording field 11, the circuit 25outputs a signal indicating the user data recording field 11 to thedrive control circuit 26 (ST3).

Then, the drive control circuit 26 outputs a selection signal to thePRML signal processing circuit 24 (ST4).

In step ST2, if the signal determining circuit 25 does not determine theuser data recording field 11, it outputs a signal indicating the headerfield 3, 8 to the drive control circuit 26 (ST5).

Then, the drive control circuit 26 outputs a selection signal to thelevel slice signal processing circuit 23 (ST6).

While the PRML signal processing circuit 24 or level slice signalprocessing circuit 23 is being selected by the selection signal obtainedin step ST4 or ST6, the drive control circuit 26 establishessynchronization of the format controller 26 c and records data orreproduces recorded data based on data from the signal processing systemproperly selected for each field (ST7).

At the start of correct data reproduction, the format controller 26 ccan grasp the position on the track and the determination result of thesignal determining circuit 25 is used no more.

In the above embodiment, a case wherein the signal determining circuit25 is provided in the succeeding stage of the optical pickup section 22is explained, but this is not limitative and, as shown in FIG. 24, acase wherein a signal determining circuit 36 is provided in thesucceeding stage of the error correcting section 27 can be realized inthe same manner. Portions which are the same as those of FIG. 12 aredenoted by the same reference numerals and an explanation thereof isomitted.

In the signal determining circuit 36, whether the signal now reproducedis a signal from the header field 3, 8 or a signal from the user datarecording field 11 is determined based on whether data is significant ornot. In order to determine whether the signal now reproduced is a signalfrom the header field 3, 8 or a signal from the user data recordingfield 11, an attempt is made to read out data on the assumption that oneof the fields is temporarily determined in the initial condition. When asignal is determined to be output from the temporarily determined field,significant data such as the sync code portion VFO, address mark AM canbe obtained and the position in the temporarily determined field isdetected at this time point.

In the case of a rewriting type, since no data is written in the userdata recording field 11 in some cases, it is preferable to search forsignificant data on the assumption that the header field 3, 8 istemporarily determined.

In this case, the signal determining circuit 36 determines whether datacan be read out from the header field 3, 8 based on an output from theerror correcting section 27 which is based on an output of the levelslice signal processing circuit 23 for processing the signal from theoptical pickup section 22 and determines that the field is the headerfield 3, 8 when data of the header field 3, 8 can be read out.

With the above construction, the data recording process and datareproduction process in the optical disk apparatus 21 are explained withreference to the flowchart shown in FIG. 25.

Immediately after the seeking operation by the optical pickup section 22or when the format controller 26 c deviates from the tracing path by adisturbance or the like, that is, when the format controller 26 c cannotgrasp the position on the track, the following control process iseffected.

That is, the signal determining circuit 36 outputs a signal indicatingthe header field 3, 8 to the drive control circuit 26 (ST11).

Then, the drive control circuit 26 outputs a selection signal to thelevel slice signal processing circuit 23 (ST12).

Thus, a signal from the level slice signal processing circuit 23 issupplied to the signal determining circuit 36 via the error correctingcircuit 27.

As a result, the signal determining circuit 36 determines whethersignificant data such as the sync. code portion VFO, address mark AM canbe obtained or not (ST13).

Then, the signal determining circuit 36 outputs a signal indicating theheader field 3, 8 to the drive control circuit 26 when significant datais obtained (ST14).

Then, the drive control circuit 26 sets up synchronization of the formatcontroller 26 c and records data or reproduces recorded data based ondata from the signal processing circuit properly selected for each field(ST15).

At the start of correct data reproduction, the format controller 26 ccan grasp the position on the track and the determination result of thesignal determining circuit 25 is used no more.

Next, another embodiment is explained with reference to FIGS. 26, 27. Inthis case, portions which are the same as those of FIGS. 12, 14 aredenoted by the same reference numerals and an explanation thereof isomitted.

In this embodiment, one example of the construction of the optical diskapparatus 21 is shown in a case where the recording density of theheader field 3, 8 in the linear direction is lowered (coarse) and thepit/mark length is made large to make an amplitude value large by usingthe same modulation code for the header field 3, 8 and user datarecording field 11 and writing data having no code with the minimum pitlength into the header field 3, 8.

The signal processing system on the reproducing side is constructed bytwo systems including a system (level slice signal processing circuit23′) for processing the header field 3, 8 according to the level slicesystem to detect channel data and a system (PRML signal processingcircuit 24′) for processing the user data recording field 11 accordingto the PRML signal processing system to detect channel data.

In the case of FIG. 27, the level slice signal processing circuit 23′ isconstructed by removing the PLL circuit 55 and 8-16 RLL demodulator 56from the level slice signal processing circuit 23 shown in FIG. 14 andthe PRML signal processing circuit 24′ is constructed by removing thePLL circuit 67 and 1,7 RLL demodulator 66 from the PRML signalprocessing circuit 24 shown in FIG. 14.

In the case of FIG. 26, a PLL circuit 37 and demodulator 38 which arecommonly used by the level slice signal processing circuit 23′ and PRMLsignal processing circuit 24′ are provided.

Further, the drive control circuit 26 supplies a selection signal to thelevel slice signal processing circuit 23′ or PRML signal processingcircuit 24′ according to a determination signal from the signaldetermining circuit 25 to perform the control operation so that data nowreproduced can be properly processed.

At this time, the drive control circuit 26 supplies a changeover signalfor a phase difference detecting system to a phase difference detectingcircuit 37 a in the PLL circuit 37 according to a determination signalfrom the signal determining circuit 25 to perform the control operationso that data now reproduced can be properly processed. Thus, the phasedifference detecting circuit 37 a in the PLL circuit 37 generates aclock for reproduction while a phase difference is detected by a phasedifference detecting system (detection of a phase difference by thelevel slice system or detection of a phase difference by the PRMLsystem) suitably selected for the level slice signal processing circuit23′ or PRML signal processing circuit 24′.

As a result, after channel data is detected, the data is demodulated bythe common demodulator 38.

Next, with the above construction, the data recording process and datareproduction process in the optical disk apparatus 21 are explained withreference to the flowchart shown in FIG. 28.

Immediately after the seeking operation of the optical pickup section 22or when the format controller 26 c deviates from the tracing path by adisturbance or the like, that is, when the format controller 26 c cannotgrasp the position on the track, the following control process iseffected.

That is, the signal determining circuit 25 checks the signal level of asignal supplied from the optical pickup section 22 (ST1) and determineswhether or not it is the recording field 11 for recording user data(ST2).

As a result of determination, if the signal determining circuit 25determines that it is the user data recording field 11, the circuit 25outputs a signal indicating the user data recording field 11 to thedrive control circuit 26 (ST3).

Then, the drive control circuit 26 outputs a selection signal to thePRML signal processing circuit 24′ and phase difference detectingcircuit 37 a (ST4′).

In step ST2, if the signal determining circuit 25 does not determine theuser data recording field 11, it outputs a signal indicating the headerfield 3, 8 to the drive control circuit 26 (ST5).

Then, the drive control circuit 26 outputs a selection signal to thelevel slice signal processing circuit 23 and phase difference detectingcircuit 37 a (ST6′).

While the PRML signal processing circuit 24 or level slice signalprocessing circuit 23 is being selected by the selection signal obtainedin step ST4′ or ST6′, the drive control circuit 26 sets upsynchronization of the format controller 26 c and records data orreproduces recorded data based on data from the signal processing systemproperly selected for each field (ST7).

When data starts to be correctly reproduced, the format controller 26 ccan grasp the position on the track and the determination result of thesignal determining circuit 25 is used no more.

Next, another embodiment is explained with reference to FIG. 29. In theabove embodiment, the header field 3, 8 is constructed by four headerfields and only one address mark AM is provided before the addressportion PID in each of the header fields, but this is not limitativeand, in another embodiment, a plurality of address marks AM can beprovided in one header field.

The layout of a header field 71 is shown in FIG. 29. In the format ofthe header field 3, 8, four header fields are provided, but in thisexample, it is assumed that only one header field 71 is provided forsimplicity, but this does not limit the number of header fields 71.

The header field 71 has a significant feature in that AM (address mark)patterns for detecting divisions between data items are recorded in aplurality of portions of the same header field 71.

The header field 71 is constructed of 49 bytes and includes a 36-bytesync code portion VFO (Variable Frequency Oscillator), 3-byte addressmark AM, 4-byte address portion PID (Position Identifier), 2-byte errordetection code IED (ID Error Detection Code), one-byte post amble PA and3-byte address mark AM arranged in this order from the left side.

With the above construction, the reliability at the time of reproductionof information recorded in the header field 71 can be significantlyenhanced. That is, as shown in FIG. 29, in this embodiment, the addressmarks AM for attaining data byte synchronization are respectivelyprovided before the address portion PID and after the post amble PA.

Generally, synchronization is attained by use of the address mark AMprovided before the address portion PID to take out succeedingindividual information items and, if no error is detected by the errordetection code, it is supposed that correct sector information andsector number can be obtained.

In this embodiment, even if an error is detected by use of the errordetection code, correct sector information and sector number can beobtained by use of the following means in a case where the detectionerror is caused only by use of the address mark AM provided before theaddress portion PID. Since the address mark AM provided before theaddress portion PID is placed in position immediately after the synccode portion VFO, a detection error tends to occur when the pull-inprocess of the PLL is delayed by a disturbance. However, even in such acase, data after the address portion PID is correctly read out in somecases.

Next, an ID detecting circuit 80 for detecting the address portion PIDin a case where one header field 71 has two address marks AM isexplained with reference to FIGS. 30, 31.

FIG. 30 shows the circuit construction of the ID detecting circuit 80and FIG. 31 is a circuit construction diagram of the optical diskapparatus 21 having the ID detecting circuit 80 mounted thereon. In thecase of FIG. 31, portions which are the same as those of FIGS. 12, 14are denoted by the same reference numerals and an explanation thereof isomitted. However, it should be noted that the changeover switches 59 inthe signal determining circuit 25 and level slice signal processingcircuit 23 and the changeover switch 70 in the PRML signal processingcircuit 24 are omitted.

As shown in FIG. 31, the ID detecting circuit 80 is provided in thesucceeding stage of the 8-16 RLL demodulator 56 which is the last stageof the level slice signal processing circuit 23 for processing thesignal from the header field, detects ID information based on binarydata decoded by the 8-16 RLL demodulator 56 and the channel clock fromthe PLL circuit 55 and outputs the detected ID information to the drivecontrol circuit 26.

As shown in FIG. 30, the ID detecting circuit 80 includes a shiftregister 81, address mark detector (AM detector) 82, counter 83, IDinformation detector 84, stack register 85, changeover switches 86 a, 86b and stack counter 87.

The shift register 81 is supplied with channel bit data as binary datadecoded by the 8-16 RLL demodulator 56 at an input terminal 81 a andshifts the channel bit data for each bit to the left direction in thedrawing in synchronism with the channel clock. The shift register 81 isrequired to have at least the length capable of receiving all of thedata of the header field 71 and is required to have a margin so as tosave data for recovery when the first address mark AM fails to bedetected and store the whole data even if the data is shifted due to theoccurrence of an error. For example, the shift register has a margin ofseveral bytes to several tens of bytes in addition to the data number of49 bytes of the header field 71.

The AM detector 82 detects an address mark AM based on the coincidencebetween AM patterns.

The counter 83 notifies that one-byte data is taken out and supplied tothe ID information detector 84 for every 16 bits.

The ID information detector 84 recovers sector information and sectornumber from the readout channel bit pattern and detects an error.

Further, the ID information detector 84 outputs an instruction to the AMdetector 82 again to detect the address mark AM when the error detectioncode IED reading operation is ended so as to make ready for a casewherein an error occurs.

The stack register 85 stacks a lower 16-bit channel data pattern of theshift register 81 supplied via the switch 86 a.

The changeover switches 86 a, 86 b are set on a node 86 d side when thetop of the stacked data becomes the head address of the address portionPID and puts the contents of the stack register 85 into the IDinformation detector 84.

The stack counter 87 counts the bytes (=16 channel bits) after the shiftregister starts to reverse the shifting direction and detects the depthof the stacked data until the top of the stacked data becomes the headaddress of the address portion PID.

With the above construction, the detection process of the ID detectingcircuit 80 is explained with reference to the flowchart shown in FIG.33.

A signal for starting detection of the address mark AM is supplied fromthe format controller 26 c to the AM detector 82 approximately at a timepoint when the header field is subjected to the read process and the PLLoperation starts to be converged according to the VFO pattern. At thesame time, data of the ID field starts to be input to the input terminal81 a of the shift register 81 (ST21). Thus, readout channel bit data isinput to the shift register 81 via the input terminal 81 a and shiftedfor each bit to the left direction in FIG. 33 in synchronism with thechannel clock.

In this case, it is assumed that data has been subjected to 8-16modulation in the header field 3, 8, for example. Since the address markAM is 3 bytes, it is 48 bits in the channel code.

When coincidence of the 48-bit pattern is detected in the AM detector82, the AM pattern is detected (ST22) and an enable signal is output tothe counter 83 via a signal line 88. As a result, the counter 83 is setinto the enable state and starts to count the channel clock. Sinceone-byte data corresponds to a 16-bit code on the channel, the counter83 informs the ID information detector 84 that one-byte data is takenout for every 16 bits.

At this time, the changeover switches 86 a, 86 b are set on the node 86c side to permit lower 16-bit data of the shift register 81 to be inputas it is to the ID information detector 84 (ST23).

The ID information detector 84 recovers the sector information andsector number from the readout channel bit pattern and detects an error(ST24). If no error is detected, a process for starting access to thesector or a process for making preparation for detection of the nextsector is performed by the same operation as in the conventional case(ST25).

When detecting the address mark AM provided after the post amble PA, theAM detector 82 resets the counter 83 by use of a signal supplied via thesignal line 88, and at the same time, reverses the shifting direction ofthe shift register 81 by use of the signal from the signal line 89. Thecounter 83 re-starts to count the channel clock and supplies a latchsignal to the stack register 85 for every 16 bits.

As a result, the lower 16-bit channel data pattern of the shift register81 is pushed into the stack register 85 via the switch 86 a. When theshifting direction of the shift register 81 starts to be reversed, theswitch 86 a is set on the node 86 d side to permit lower 16-bit data ofthe shift register 81 to be supplied to the stack register 85.

The stack counter 87 counts bytes (=16 channel bits) after the shiftingdirection of the shift register 81 starts to be reversed and detects thedepth of the stacked data until the top of the stacked data becomes thehead address of the address portion PID. When the top of the stackeddata becomes the head address of the address portion PID, the switches86 a, 86 b are set on the node 86 d side so as to put the contents ofthe stack register 85 into the ID information detector 84 (ST27).

The ID information detector 84 recovers sector information and sectornumber from the readout channel bit pattern and detects an error (ST28).

If no error is detected, a process for starting access to the sector ora process for making preparation for detection of the next sector isperformed by use of the above information by the same operation as inthe conventional case.

Since the operation after the shifting direction of the sift register 81is reversed is a retrial operation using the address mark AM provided inthe rear portion when an error occurs in the first ID detection process,the operation can be stopped at any point in time if the first IDdetection process is successfully effected.

In this embodiment, the other address mark AM is provided after theerror detection code IED. Therefore, the ID information detector 84outputs an instruction to the AM detector 82 again to detect the addressmark AM when the error detection code IED reading operation is ended soas to make ready for a case wherein an error occurs. As shown in thesteps ST31 to ST33 of FIG. 33, it is possible to detect the otheraddress mark AM before the error detection result is determined bytaking the detection time of the error detection code IED intoconsideration.

In the above embodiment, the address marks AM are distributed andarranged in two portions of the same header field, but this is notlimitative and the same operation can be attained even if address marksAM are distributed and arranged in three or more portions of the sameheader field.

Next, another embodiment in which the contents of the header field arechanged depending on the sector is explained. Generally, when therecording density in the header field is lowered, the header field ismade longer if the amount of ID information is not reduced, but in thisembodiment, an increase in the length of the header field is suppressedby reducing an amount of ID information in the header field for eachsector.

As one example, one ECC block is constructed by 16 2-kilobyte sectors inthe optical disk 1 used for a DVD as shown in FIG. 8, but in this case,ID information (refer to FIG. 29) identical to that in the conventionalcase is recorded in the header field 3, 8 of the head sector of the ECCblock and only the sector number or track number is recorded in theheader field 3, 8 of the other sectors.

As another example, if ID information is constructed by four bytes asshown in FIG. 34, the amount of ID information is reduced by recordingthe least significant one byte in the header field of each sector anddistributing and recording the remaining three bytes in the respectivesectors.

A more specific example is shown in FIG. 35. A header field of theconventional form in which ID information is constructed by four bytesof ID information 1 to ID information 4, the contents of the IDinformation 1 is “00010100”, the contents of the ID information 2 is“11001001”, the contents of the ID information 3 is “00111101” and thecontents of the ID information 4 is “01100001” is considered and anexample of ID information of a form based on this embodiment andcorresponding to the above form is shown.

It is supposed that three successive sectors each having a header fieldto which the ID information of this embodiment is applied are provided.In the header field of the first sector, only the ID information 1 andID information 4 of the header of the conventional form are recorded.That is, the contents of binary data recorded in the header field become“00010100”+“01100001”. Only binary data obtained by incrementing thecontents of the ID information 4 by one and the ID information 2 of theheader of the conventional form are recorded in the header of the secondsector.

That is, the contents of the binary data recorded in the header fieldbecome “11001001”+“01100010”. The reason why the contents of the secondbyte become a value obtained by incrementing the contents of the IDinformation 4 of the header field of the conventional form by one isthat the ID information 4 is supposed to be the least significant byteof the sector number and the sector number is incremented by one. Onlybinary data obtained by incrementing the contents of the ID information4 by two and the ID information 3 of the header of the conventional formare recorded in the header of the third sector. That is, the contents ofbinary data recorded in the header field become “00111101”+“01100011”.

In this embodiment, since the whole portion of the ID information cannotbe obtained simply by reading one header field, it takes a long time toobtain a correct sector number (block number), for example. However, ina conventional ID information recording method, when access is made to alarge number of successive header fields, the amount of information in aredundant portion and readout time of the header field become uselesssince most of the ID information is not so different in the adjacentheader fields.

In this embodiment, information which varies for each header field isrecorded in each header field and information of a portion which doesnot change is distributed in a plurality of header fields so as toenhance the efficiency of the readout time and information amount.

As still another example, a system for supporting additional writing andrewriting of written data is considered as a recording/reproducingoptical disk. That is, the system is a system in which new data can beadditionally written in a portion immediately after a data field inwhich significant data is written, data cannot be jumped to and writteninto a field successive to a data field in which data has not beenwritten and the contents of a data field in which data has been alreadywritten can be rewritten. Since data exists in the lead-in field of theoptical disk to which access is first made, initial writing can beperformed immediately after this field.

In the optical disk system with the above construction, addressinformation can be eliminated from the header field. Since IDinformation is recorded together with user data in the sector or ECCblock in which data is already written, the access position can bedetected by reading out the above data. It is only required to record apattern used for synchronization of the start position of the sector(block) in the header field.

As described above, a signal of the conventional level slice system canbe detected and detection delay time can be reduced by setting therecording density of the header field in the linear direction lower(coarse) than that of the user data recording field.

Further, a signal of the conventional level slice system can be detectedand detection delay time can be reduced by using the mark position formhaving a large detection margin as the information recording system ofthe header field.

Further, a readout error of the sector number due to a detection errorcan be compensated for by recording the address marks AM for attainingbyte synchronization of the header field in both of the head portion andtail portion of information recorded in the header field.

Thus, it becomes possible to provide an optical disk which has a largecapacity and is high in reliability and in which the length of theto-be-changed field is reduced to improve the format efficiency bysuppressing the readout delay of the sector number of the header fieldand a readout error of the sector number due to a detection error of thedata dividing pattern in the header field can be compensated for.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. An optical disc, comprising: a first area including first data formedas pre-pit data; and a second area including second data formed as otherpre-pit data, a minimum pit length of the first data being based on a 2Tsystem, the first data being measured by a slicer, a minimum pit lengthof the second data being based on the 2T system, the second data beingrecorded in such a manner as to be detected in partial response andmaximum likelihood (PRML) detecting system.